Painted in 1781, Fuseli's The Nightmare is the founding image of Gothic-Romantic visualization of dream and the unconscious. A young woman lies sleeping across a bed, her body arched backwards in unrest; a squat demon (an incubus) crouches on her chest; a wild-eyed horse — the 'mare' of the title's pun — leans through a curtain at the bedside, mouth open. The painting was Fuseli's first major public sensation at the 1782 Royal Academy exhibition; it shocked viewers and was widely reproduced in print form.

Fuseli (Johann Heinrich Füssli, 1741-1825) was a Swiss-born painter who spent most of his career in England, where he was a close friend of William Blake and tutor to many of the second-generation Romantic painters. The Nightmare condenses the eighteenth-century iconography of sleep, sexual anxiety, and Germanic folklore into a single composition that prefigures Freud's psychoanalytic understanding of the dream by 120 years and the Symbolist movement by 110 years. Sigmund Freud kept a print of it in his consulting rooms.

The painting hangs in the Detroit Institute of Arts. A second version (1790-91) is held by the Goethe Museum in Frankfurt. The image has become the canonical visual referent for the word 'nightmare' in Anglophone culture, reproduced in twentieth-century horror cinema, album covers, and academic histories of psychology.